Recently, in a display device typified by a liquid crystal display device, an optical sensor is mounted in some cases for automatically adjust brightness of its display screen according to intensity of light around the display device. A display device in which a plurality of optical sensors are provided in matrix is known as well. In this display device, the plurality of optical sensors function as one area sensor so as to capture an image on a side to an observer.
The mounting of the optical sensor in the display device can be achieved by mounting an optical sensor as a discrete component on the display panel. Alternatively, the optical sensor may be formed monolithically with an active matrix substrate, through a process of forming active elements (TFTs) or peripheral circuits.
Among these, in the field of the display device for portable terminal devices in particular, the optical sensor is required to be formed monolithically with the active matrix substrate, from the viewpoint of reducing the number of components and reducing the size of the display device. As the optical sensor formed monolithically, for example, a photodiode formed of a silicon film is known (see, e.g., JP2006-3857A).
Here, the following explains the conventional photodiode (optical sensor), while referring to FIG. 20. FIG. 20 is a cross-sectional view showing a configuration of a conventional liquid crystal display panel provided with a photodiode. As shown in FIG. 20, a photodiode 51 is a PIN diode having a lateral structure, and is formed monolithically with an active matrix substrate 51 that composes a liquid crystal display panel.
As shown in FIG. 20, the photodiode 51 is provided with a silicon film 60. The silicon film 60 is formed on a glass substrate 52 as a base substrate of an active matrix substrate 50 simultaneously with a thin film transistor (TFT) functioning as an active element, through a process for forming the thin film transistor (TFT). In the silicon film 60, an n-type semiconductor region (n-layer) 51a, an intrinsic semiconductor region (i-layer) 51b, and a p-type semiconductor region (p-layer) 51c are provided in the stated order in a planar direction. The i-layer 51b becomes a photodetecting region of the photodiode 51.
In a layer below the photodiode 51, a light shielding film 53 for blocking illumination light from a backlight device (not shown) is provided. The light shielding film 53 is covered with an insulative basecoat 54. The light shielding film 53 is usually made of a metal material. The conventional light shielding film 53 is in an electrically floating state, being insulated from the surroundings. Further, the photodiode 51 is covered with interlayer insulation films 55 and 56.
It should be noted that in FIG. 20, “57” indicates a line connected to an n-layer 51a, and “58” indicates a line connected to a p-layer 51c. “59” indicates a flattening film, and “61” indicates a protective film. “62” indicates a liquid crystal layer. As to a filter substrate 63, only an outline is illustrated.